Abstract：This study aims to investigate experimentally the relation between dynamic damage state and mechanics responses of a red sandstone. Cracks and holes on the surface of specimen are observed and recorded synchronously with deformation responses. The images of cracking of specimen in different water content states are analyzed by a digital image technique，and quantitative results for surface cracking process are obtained. In order to obtain the quantitative description of microcosmically prefabricated cracks development，two physical quantities，of damage tensor and crack degree，are proposed for quantitatively estimating dynamic and gradual damage development of the red sandstone using microcosmic cracking in water content state. Further understanding about the damage evolution law of red sandstone under single axis compression though applying microstructure method is also obtained.
